Rotating offline DS units

ABSTRACT

A method begins by a computing device of a dispersed storage network (DSN) selectively bringing online and taking offline storage units of a set of storage units of the DSN. When bringing a first storage unit of the set of storage units online and taking a second storage unit of the set of storage units offline in accordance with the selectively bringing online and taking offline storage units, the method continues with the computing device determining a rebuilding approach of the first storage unit and a first to second storage unit transition. The method continues with the computing device bringing the first storage unit online in accordance with the rebuilding approach and the first to second storage unit transition and taking the second storage unit offline in accordance with the first to second storage unit transition.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present U.S. Utility Patent Applications claims priority pursuant to35 U.S.C. § 120, as a continuation-in-part to U.S. Utility patentapplication Ser. No. 15/425,128, entitled “DETECTION AND CORRECTION OFCOPY ERRORS IN A DISTRIBUTED STORAGE NETWORK”, filed Feb. 6, 2017, whichis a continuation of U.S. Utility patent application Ser. No.14/320,547, entitled “UPDATING DE-DUPLICATION TRACKING DATA FOR ADISPERSED STORAGE NETWORK”, filed Jun. 30, 2014, now issued as U.S. Pat.No. 9,661,074, which claims priority pursuant to 35 U.S.C. § 119(e) toU.S. Provisional Application No. 61/871,833, entitled “PRIORITIZING DATARETENTION IN A DISPERSED STORAGE NETWORK”, filed Aug. 29, 2013, all ofwhich are hereby incorporated herein by reference in their entirety forall purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not Applicable.

BACKGROUND OF THE INVENTION Technical Field of the Invention

This invention relates generally to computer networks and moreparticularly to rotating offline storage units of a dispersed storagenetwork.

Description of Related Art

Computing devices are known to communicate data, process data, and/orstore data. Such computing devices range from wireless smart phones,laptops, tablets, personal computers (PC), work stations, and video gamedevices, to data centers that support millions of web searches, stocktrades, or on-line purchases every day. In general, a computing deviceincludes a central processing unit (CPU), a memory system, userinput/output interfaces, peripheral device interfaces, and aninterconnecting bus structure.

As is further known, a computer may effectively extend its CPU by using“cloud computing” to perform one or more computing functions (e.g., aservice, an application, an algorithm, an arithmetic logic function,etc.) on behalf of the computer. Further, for large services,applications, and/or functions, cloud computing may be performed bymultiple cloud computing resources in a distributed manner to improvethe response time for completion of the service, application, and/orfunction. For example, Hadoop is an open source software framework thatsupports distributed applications enabling application execution bythousands of computers.

In addition to cloud computing, a computer may use “cloud storage” aspart of its memory system. As is known, cloud storage enables a user,via its computer, to store files, applications, etc. on an Internetstorage system. The Internet storage system may include a RAID(redundant array of independent disks) system and/or a dispersed storagesystem that uses an error correction scheme to encode data for storage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 is a schematic block diagram of an embodiment of a dispersed ordistributed storage network (DSN) in accordance with the presentinvention;

FIG. 2 is a schematic block diagram of an embodiment of a computing corein accordance with the present invention;

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data in accordance with the present invention;

FIG. 4 is a schematic block diagram of a generic example of an errorencoding function in accordance with the present invention;

FIG. 5 is a schematic block diagram of a specific example of an errorencoding function in accordance with the present invention;

FIG. 6 is a schematic block diagram of an example of a slice name of anencoded data slice (EDS) in accordance with the present invention;

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of data in accordance with the present invention;

FIG. 8 is a schematic block diagram of a generic example of an errordecoding function in accordance with the present invention;

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network in accordance with the present invention;

FIG. 10 is a flowchart illustrating an example of selecting activestorage units in accordance with the present invention;

FIG. 11 is a flowchart illustrating an example of enabling slicerebuilding in accordance with the present invention;

FIG. 12 is a schematic block diagram of an example of selectivelybringing online and taking offline storage units in accordance with thepresent invention; and

FIG. 13 is a flowchart illustrating an example of rotating offlinestorage units of a dispersed storage network (DSN) in accordance withthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a schematic block diagram of an embodiment of a dispersed, ordistributed, storage network (DSN) 10 that includes a plurality ofcomputing devices 12-16, a managing unit 18, an integrity processingunit 20, and a DSN memory 22. The components of the DSN 10 are coupledto a network 24, which may include one or more wireless and/or wirelined communication systems; one or more non-public intranet systemsand/or public internet systems; and/or one or more local area networks(LAN) and/or wide area networks (WAN).

The DSN memory 22 includes a plurality of storage units 36 that may belocated at geographically different sites (e.g., one in Chicago, one inMilwaukee, etc.), at a common site, or a combination thereof. Forexample, if the DSN memory 22 includes eight storage units 36, eachstorage unit is located at a different site. As another example, if theDSN memory 22 includes eight storage units 36, all eight storage unitsare located at the same site. As yet another example, if the DSN memory22 includes eight storage units 36, a first pair of storage units are ata first common site, a second pair of storage units are at a secondcommon site, a third pair of storage units are at a third common site,and a fourth pair of storage units are at a fourth common site. Notethat a DSN memory 22 may include more or less than eight storage units36. Further note that each storage unit 36 includes a computing core (asshown in FIG. 2, or components thereof) and a plurality of memorydevices for storing dispersed error encoded data.

Each of the computing devices 12-16, the managing unit 18, and theintegrity processing unit 20 include a computing core 26, which includesnetwork interfaces 30-33. Computing devices 12-16 may each be a portablecomputing device and/or a fixed computing device. A portable computingdevice may be a social networking device, a gaming device, a cell phone,a smart phone, a digital assistant, a digital music player, a digitalvideo player, a laptop computer, a handheld computer, a tablet, a videogame controller, and/or any other portable device that includes acomputing core. A fixed computing device may be a computer (PC), acomputer server, a cable set-top box, a satellite receiver, a televisionset, a printer, a fax machine, home entertainment equipment, a videogame console, and/or any type of home or office computing equipment.Note that each of the managing unit 18 and the integrity processing unit20 may be separate computing devices, may be a common computing device,and/or may be integrated into one or more of the computing devices 12-16and/or into one or more of the storage units 36.

Each interface 30, 32, and 33 includes software and hardware to supportone or more communication links via the network 24 indirectly and/ordirectly. For example, interface 30 supports a communication link (e.g.,wired, wireless, direct, via a LAN, via the network 24, etc.) betweencomputing devices 14 and 16. As another example, interface 32 supportscommunication links (e.g., a wired connection, a wireless connection, aLAN connection, and/or any other type of connection to/from the network24) between computing devices 12 & 16 and the DSN memory 22. As yetanother example, interface 33 supports a communication link for each ofthe managing unit 18 and the integrity processing unit 20 to the network24.

Computing devices 12 and 16 include a dispersed storage (DS) clientmodule 34, which enables the computing device to dispersed storage errorencode and decode data 40 as subsequently described with reference toone or more of FIGS. 3-8. In this example embodiment, computing device16 functions as a dispersed storage processing agent for computingdevice 14. In this role, computing device 16 dispersed storage errorencodes and decodes data (e.g., data 40) on behalf of computing device14. With the use of dispersed storage error encoding and decoding, theDSN 10 is tolerant of a significant number of storage unit failures (thenumber of failures is based on parameters of the dispersed storage errorencoding function) without loss of data and without the need for aredundant or backup copies of the data. Further, the DSN 10 stores datafor an indefinite period of time without data loss and in a securemanner (e.g., the system is very resistant to unauthorized attempts ataccessing the data).

In operation, the managing unit 18 performs DS management services. Forexample, the managing unit 18 establishes distributed data storageparameters (e.g., vault creation, distributed storage parameters,security parameters, billing information, user profile information,etc.) for computing devices 12-14 individually or as part of a group ofuser devices. As a specific example, the managing unit 18 coordinatescreation of a vault (e.g., a virtual memory block associated with aportion of an overall namespace of the DSN) within the DSTN memory 22for a user device, a group of devices, or for public access andestablishes per vault dispersed storage (DS) error encoding parametersfor a vault. The managing unit 18 facilitates storage of DS errorencoding parameters for each vault by updating registry information ofthe DSN 10, where the registry information may be stored in the DSNmemory 22, a computing device 12-16, the managing unit 18, and/or theintegrity processing unit 20.

The DSN managing unit 18 creates and stores user profile information(e.g., an access control list (ACL)) in local memory and/or withinmemory of the DSN memory 22. The user profile information includesauthentication information, permissions, and/or the security parameters.The security parameters may include encryption/decryption scheme, one ormore encryption keys, key generation scheme, and/or dataencoding/decoding scheme.

The DSN managing unit 18 creates billing information for a particularuser, a user group, a vault access, public vault access, etc. Forinstance, the DSTN managing unit 18 tracks the number of times a useraccesses a non-public vault and/or public vaults, which can be used togenerate a per-access billing information. In another instance, the DSTNmanaging unit 18 tracks the amount of data stored and/or retrieved by auser device and/or a user group, which can be used to generate aper-data-amount billing information.

As another example, the managing unit 18 performs network operations,network administration, and/or network maintenance. Network operationsincludes authenticating user data allocation requests (e.g., read and/orwrite requests), managing creation of vaults, establishingauthentication credentials for user devices, adding/deleting components(e.g., user devices, storage units, and/or computing devices with a DSclient module 34) to/from the DSN 10, and/or establishing authenticationcredentials for the storage units 36. Network administration includesmonitoring devices and/or units for failures, maintaining vaultinformation, determining device and/or unit activation status,determining device and/or unit loading, and/or determining any othersystem level operation that affects the performance level of the DSN 10.Network maintenance includes facilitating replacing, upgrading,repairing, and/or expanding a device and/or unit of the DSN 10.

The integrity processing unit 20 performs rebuilding of ‘bad’ or missingencoded data slices. At a high level, the integrity processing unit 20performs rebuilding by periodically attempting to retrieve/list encodeddata slices, and/or slice names of the encoded data slices, from the DSNmemory 22. For retrieved encoded slices, they are checked for errors dueto data corruption, outdated version, etc. If a slice includes an error,it is flagged as a ‘bad’ slice. For encoded data slices that were notreceived and/or not listed, they are flagged as missing slices. Badand/or missing slices are subsequently rebuilt using other retrievedencoded data slices that are deemed to be good slices to produce rebuiltslices. The rebuilt slices are stored in the DSTN memory 22.

FIG. 2 is a schematic block diagram of an embodiment of a computing core26 that includes a processing module 50, a memory controller 52, mainmemory 54, a video graphics processing unit 55, an input/output (IO)controller 56, a peripheral component interconnect (PCI) interface 58,an IO interface module 60, at least one IO device interface module 62, aread only memory (ROM) basic input output system (BIOS) 64, and one ormore memory interface modules. The one or more memory interfacemodule(s) includes one or more of a universal serial bus (USB) interfacemodule 66, a host bus adapter (HBA) interface module 68, a networkinterface module 70, a flash interface module 72, a hard drive interfacemodule 74, and a DSN interface module 76.

The DSN interface module 76 functions to mimic a conventional operatingsystem (OS) file system interface (e.g., network file system (NFS),flash file system (FFS), disk file system (DFS), file transfer protocol(FTP), web-based distributed authoring and versioning (WebDAV), etc.)and/or a block memory interface (e.g., small computer system interface(SCSI), internet small computer system interface (iSCSI), etc.). The DSNinterface module 76 and/or the network interface module 70 may functionas one or more of the interface 30-33 of FIG. 1. Note that the 10 deviceinterface module 62 and/or the memory interface modules 66-76 may becollectively or individually referred to as IO ports.

FIG. 3 is a schematic block diagram of an example of dispersed storageerror encoding of data. When a computing device 12 or 16 has data tostore it disperse storage error encodes the data in accordance with adispersed storage error encoding process based on dispersed storageerror encoding parameters. The dispersed storage error encodingparameters include an encoding function (e.g., information dispersalalgorithm, Reed-Solomon, Cauchy Reed-Solomon, systematic encoding,non-systematic encoding, on-line codes, etc.), a data segmentingprotocol (e.g., data segment size, fixed, variable, etc.), and per datasegment encoding values. The per data segment encoding values include atotal, or pillar width, number (T) of encoded data slices per encodingof a data segment i.e., in a set of encoded data slices); a decodethreshold number (D) of encoded data slices of a set of encoded dataslices that are needed to recover the data segment; a read thresholdnumber (R) of encoded data slices to indicate a number of encoded dataslices per set to be read from storage for decoding of the data segment;and/or a write threshold number (W) to indicate a number of encoded dataslices per set that must be accurately stored before the encoded datasegment is deemed to have been properly stored. The dispersed storageerror encoding parameters may further include slicing information (e.g.,the number of encoded data slices that will be created for each datasegment) and/or slice security information (e.g., per encoded data sliceencryption, compression, integrity checksum, etc.).

In the present example, Cauchy Reed-Solomon has been selected as theencoding function (a generic example is shown in FIG. 4 and a specificexample is shown in FIG. 5); the data segmenting protocol is to dividethe data object into fixed sized data segments; and the per data segmentencoding values include: a pillar width of 5, a decode threshold of 3, aread threshold of 4, and a write threshold of 4. In accordance with thedata segmenting protocol, the computing device 12 or 16 divides the data(e.g., a file (e.g., text, video, audio, etc.), a data object, or otherdata arrangement) into a plurality of fixed sized data segments (e.g., 1through Y of a fixed size in range of Kilo-bytes to Tera-bytes or more).The number of data segments created is dependent of the size of the dataand the data segmenting protocol.

The computing device 12 or 16 then disperse storage error encodes a datasegment using the selected encoding function (e.g., Cauchy Reed-Solomon)to produce a set of encoded data slices. FIG. 4 illustrates a genericCauchy Reed-Solomon encoding function, which includes an encoding matrix(EM), a data matrix (DM), and a coded matrix (CM). The size of theencoding matrix (EM) is dependent on the pillar width number (T) and thedecode threshold number (D) of selected per data segment encodingvalues. To produce the data matrix (DM), the data segment is dividedinto a plurality of data blocks and the data blocks are arranged into Dnumber of rows with Z data blocks per row. Note that Z is a function ofthe number of data blocks created from the data segment and the decodethreshold number (D). The coded matrix is produced by matrix multiplyingthe data matrix by the encoding matrix.

FIG. 5 illustrates a specific example of Cauchy Reed-Solomon encodingwith a pillar number (T) of five and decode threshold number of three.In this example, a first data segment is divided into twelve data blocks(D1-D12). The coded matrix includes five rows of coded data blocks,where the first row of X11-X14 corresponds to a first encoded data slice(EDS 1_1), the second row of X21-X24 corresponds to a second encodeddata slice (EDS 2_1), the third row of X31-X34 corresponds to a thirdencoded data slice (EDS 3_1), the fourth row of X41-X44 corresponds to afourth encoded data slice (EDS 4_1), and the fifth row of X51-X54corresponds to a fifth encoded data slice (EDS 5_1). Note that thesecond number of the EDS designation corresponds to the data segmentnumber.

Returning to the discussion of FIG. 3, the computing device also createsa slice name (SN) for each encoded data slice (EDS) in the set ofencoded data slices. A typical format for a slice name 80 is shown inFIG. 6. As shown, the slice name (SN) 80 includes a pillar number of theencoded data slice (e.g., one of 1-T), a data segment number (e.g., oneof 1-Y), a vault identifier (ID), a data object identifier (ID), and mayfurther include revision level information of the encoded data slices.The slice name functions as, at least part of, a DSN address for theencoded data slice for storage and retrieval from the DSN memory 22.

As a result of encoding, the computing device 12 or 16 produces aplurality of sets of encoded data slices, which are provided with theirrespective slice names to the storage units for storage. As shown, thefirst set of encoded data slices includes EDS 1_1 through EDS 5_1 andthe first set of slice names includes SN 1_1 through SN 5_1 and the lastset of encoded data slices includes EDS 1_Y through EDS 5_Y and the lastset of slice names includes SN 1_Y through SN 5_Y.

FIG. 7 is a schematic block diagram of an example of dispersed storageerror decoding of a data object that was dispersed storage error encodedand stored in the example of FIG. 4. In this example, the computingdevice 12 or 16 retrieves from the storage units at least the decodethreshold number of encoded data slices per data segment. As a specificexample, the computing device retrieves a read threshold number ofencoded data slices.

To recover a data segment from a decode threshold number of encoded dataslices, the computing device uses a decoding function as shown in FIG.8. As shown, the decoding function is essentially an inverse of theencoding function of FIG. 4. The coded matrix includes a decodethreshold number of rows (e.g., three in this example) and the decodingmatrix in an inversion of the encoding matrix that includes thecorresponding rows of the coded matrix. For example, if the coded matrixincludes rows 1, 2, and 4, the encoding matrix is reduced to rows 1, 2,and 4, and then inverted to produce the decoding matrix.

FIG. 9 is a schematic block diagram of another embodiment of a dispersedstorage network (DSN) that includes a distributed storage and tasknetwork (DSTN) managing unit 98 and a set of DST execution units 1-n.Each DST execution unit may be implemented utilizing the storage unit 36of FIG. 1. The DSTN managing unit may be implemented by utilizing themanaging unit 18 of FIG. 1.

In an example of operation, the DSTN managing unit 98 obtains statusinformation from the set of DST execution units 1-n as statusinformation 1-n. The status information includes one or more of anavailability indicator, an active indicator, a required for a rebuildingindicator, a requiring rebuilding indicator, identifiers of DSTexecution units required for rebuilding, the number of pending dataaccess requests, a number of pending processing requests, and powerutilization level information. The obtaining includes at least one ofissuing a query, receiving a query response, receiving an error message,receiving an activation chain status response, and accessing ahistorical record.

The DSTN managing unit 98 selects a DST execution unit associated withan inactive status for reactivation in accordance with a rotation schemeand based on the status information, where a number of remaining DSTexecution units of the set of DST execution units is greater than orequal to a decode threshold number. The rotation scheme includes atleast one of a round-robin scheme, an equal amount of downtime, and anequal amount of utilization. The selecting may be based on one or moreof a power utilization level, a desired power utilization level, anumber of desired active units, a desired reliability level, a desiredavailability level, and DST execution unit capabilities.

With the DST execution unit for reactivation selected, the DSTN managingunit 98 issues an activation status change request to the selected DSTexecution unit. The activation status change request includes one ormore of a DST execution unit ID, a requested status (e.g., not active,active), and a status transition approach (e.g., immediately, at ascheduled future timeframe, when no current or pending data accessrequest exists, when no current or pending rebuilding activity exists).As a specific example, the activation status change request includes arequest to reactivate and a transition approach for immediate transition(e.g., alternatively for a scheduled transition in accordance with atleast one of a transition schedule and a request).

The DSTN managing unit 98 receives a favorable activation status changeresponse from the selected DST execution unit for reactivation. Theactivation status change response includes one or more of the DSTexecution unit identifier, the requested status, the actual status, anumber of current or pending data access requests, a number of currentor pending rebuilding tasks, and an estimated time to status transitionwhen not immediate. As a specific example, the activation status changeresponse includes an indicator that the DST execution unit is nowactive.

With the DST execution units selected for reactivation now active, theDSTN managing unit 98 selects another DST execution unit associated withan active status for deactivation in accordance with the rotation schemeand based on the status information, where a number of remaining DSTexecution units of the set of DST execution units is greater than orequal to a decode threshold number. The selecting may be based on one ormore of a power utilization level, a desired power utilization level, anumber of desired active units, a desired reliability level, a desiredavailability level, DST execution unit capabilities, and identifying aDST execution unit associated with a number of pending tasks that isless than a low pending tasks threshold level (e.g., few or no pendingpartial task processing tasks, few or no pending data access tasks).

With the other DST execution units selected for deactivation, the DSTNmanaging unit 18 determines a transition approach for the other DSTexecution unit based on the status information (e.g., immediately,scheduled, after pending tasks are executed). As a specific example, theDSTN managing unit 98 determines the transition approach to be theimmediate approach when a priority of estimated power savings is greaterthan all other priorities. As another specific example, the DSTNmanaging unit 98 determines the transition approach to be after thepending tasks are executed when the pending tasks include criticalrebuilding tasks and the critical rebuilding tasks are associated with apriority that is greater than all other priorities. With the transitionapproach determined, the DSTN managing unit 98 issues and activationstatus change request to the other DST execution unit, where theactivation status change request includes the transition approach and arequest to deactivate. The method to change activation status isdiscussed in greater detail with reference to FIGS. 10 and 11.

From time to time, one or more of the DST execution units rebuildsencoded data slices associated with slice errors. The rebuildingincludes scanning for errors and remedying the errors. The DST executionunits share rebuilding information 91. The rebuilding information 91includes one or more of a list slice request, a list slice response, aread slice request, a read slice response, a partial slice request, anda partial slice response. The scanning for errors includes a DSTexecution unit associated with an active status issuing list slicerequests to other active DST execution units and receiving list sliceresponses for comparison to identify slice errors. The remedyingincludes an active DST execution unit obtaining at least a decodethreshold number of representations of encoded data slices of a set ofencoded data slices where at least one encoded data slice is associatedwith a slice error. The obtaining includes issuing one or more of readslice requests and read partial slice requests to active DST executionunits and receiving one or more of read slice responses and read partialslice responses. The obtaining further includes waiting for required DSTexecution units to become active prior to sending of the one or more ofthe read slice requests and the read partial slice requests. The methodof rebuilding is discussed in greater detail with reference to FIG. 13.

FIG. 10 is a flowchart illustrating an example of selecting activestorage units. The method continues at step 100 where a processingmodule (e.g., of a distributed storage and task network (DSTN) managingunit) obtains status information for a set of storage units. The methodcontinues at step 102 where the processing module selects a storage unitassociated with an inactive status for reactivation in accordance with arotation scheme and based on the status information. As a specificexample, the processing module selects a next storage unit of a storageunit rotation list, where the storage unit is associated with anavailable and inactive status. The method continues at step 104 wherethe processing module issues and activation status change request to theselected storage unit to reactivate the storage unit. The methodcontinues at step 106 where the processing module receives an activationstatus change response from the selected storage unit indicating thatthe storage unit has been reactivated.

When the activation status change response includes a favorableactivation status change indicator (e.g., indicating that the selectedstorage unit has been reactivated), the method continues at step 108where the processing module selects another storage unit associated withan active status for deactivation in accordance with the rotation schemeand based on the status information. As a specific example, theprocessing module selects the other storage unit where the other storageunit is associated with no pending storage or rebuilding tasks. Themethod continues at step 110 where the processing module determines atransition approach for the selected other storage unit based on thestatus information. As a specific example, the processing moduledetermines the transition approach to include transitioning afterpending tasks have been processed when the status information indicatesthat the other storage unit is associated with pending rebuilding ordata access tasks. The method continues at step 112 where the processingmodule issues and activation status change request to the selected otherstorage unit, where the request includes the transition approach and anindicator to deactivate the selected other storage unit.

FIG. 11 is a flowchart illustrating an example of enabling slicerebuilding, which includes similar steps to FIG. 10. The methodcontinues with steps 100-104 of FIG. 10 where a processing module (e.g.,of a distributed storage and task network (DSTN) managing unit) obtainsstatus information for a set of storage units, selects a storage unitassociated with an inactive status for reactivation in accordance with arotation scheme and based on the status information, and issues anactivation status change request to the selected storage unit.

The method continues at step 126 where the processing module receives anactivation status change response from the selected storage unit thatindicates detected slice errors and required candidate in active storageunits to facilitate rebuilding encoded data slices associated with thedetected slice errors. As a specific example, the selected storage unitscans for the slice errors and issues the activation status changeresponse after determining that a decode threshold number of otherstorage units are not available to facilitate rebuilding.

The method continues at step 128 where the processing module selects oneor more other storage units associated with an inactive status forreactivation based on the required candidate in active storage units andin accordance with a rotation scheme. As a specific example, theprocessing module selects a storage unit that is scheduled forreactivation soon in accordance with the rotation scheme that isincluded in the required candidate in active storage units. The methodcontinues at step 130 where the processing module issues and activationstatus change request to the one or more other storage units requestingreactivation.

The method continues with step 106 of FIG. 10 where the processingmodule receives an activation status change response from the selectedstorage unit (e.g., after rebuilding). The method continues at step 134where the processing module obtains updated status information for theset of storage units. When the activation status change responseincludes an indication that rebuilding has been completed, the methodcontinues at step 136 where the processing module selects at least oneof the one or more other storage units for deactivation in accordancewith the rotation scheme and the updated status information. As aspecific example, the processing module selects the other storage unitwhere the other storage unit is associated with no pending rebuildingtasks for the selected storage unit.

The method continues at step 138 where the processing module determinesa transition approach for the selected at least one storage unit basedon the updated status information. As a specific example, the processingmodule indicates the transition approach to be immediately sincerebuilding has been completed for the selected storage unit. As anotherspecific example, the processing module indicates the transitionapproach to be after processing of the rebuilding tasks associated withother storage units. The method continues at step 140 where theprocessing module issues an activation status change request of the atleast one storage unit, where the request includes the transitionapproach.

FIG. 12 is a schematic block diagram of an example of selectivelybringing online and taking offline storage units of a set of storageunits of a dispersed storage network (DSN). As illustrated, eightstorage units SU #1-8 36 are selectively brought online and takenoffline during five times T1-T5 (e.g., where a time interval is inminutes, hours, days, weeks, etc.). The selectively bringing online andtaking offline storage units includes one or more of a scheduledtimeframe, an amount of power consumed by a storage unit of the set ofstorage units, an amount of data written to a storage unit of the set ofstorage units, restricting taking offline a storage unit that includesan encoded data slice that needs rebuilding, restricting taking offlinea storage unit that includes an encoded data slice that is critical to arebuilding of another encoded data slice, and determining a storage unitof the set of storage units will not be available during a scheduledonline timeframe (e.g., the storage units includes one or more harddrive failures, but still may have many other functioning hard drives).

The selectively bringing online and taking offline storage units mayalso be determined according to rotation priority levels. For example, afirst rotation priority level may include restricting taking offline astorage unit that includes an encoded data slice that needs rebuilding,a second rotation priority level may include an amount of power consumedby a storage unit of the set of storage units, and a third rotationpriority level may include a scheduled timeframe. For example, when thethird rotation priority indicates that a sixth storage unit shouldremain online, the second rotation priority indicates that the sixthstorage unit should be taken offline and the first priority is null(e.g., no encoded data slices stored in the sixth storage unit neededfor rebuilding), the computing device may take the sixth storage unitoffline (e.g., due to the second rotation priority level being a highestnon-null priority).

In an example of operation, a decode threshold number is 3, a readthreshold number is 4, a write threshold number is 5 and a pillar widthnumber is 8. During a first time T1, storage units 1, 6 and 7 areoffline and storage units 2-5 and 8 are online. Also during the firsttime T1 (and any other times), a computing device may update or writesets of encoded data slices to the set of storage units according to adispersed storage network storage protocol (e.g., DS error encodingparameters). For example, encoded data slices of the sets are written tothe online storage units SU #2-5 and #7 and encoded data slices to bewritten in the offline storage units (e.g., SU #1, #6, and #7) are not.The encoded data slices for the offline storage units may be stored incache memory of a DS processing unit until the offline storage unit isavailable, sent to a proxy storage unit (e.g., an online SU) until theoffline storage unit corresponding to the encoded data slice for storageis online, and/or added to a rebuild list. In one example, when astorage unit comes online and an encoded data slice previously stored inthe newly online storage unit is determined to need rebuilding (e.g., ismissing, is outdated, etc.), a computing device may send a correspondingrebuilt encoded data slice to the newly online storage unit. As anotherexample, when a storage unit comes online, an encoded data slice of aset of encoded data slices of the newly online storage unit that isdetermined to need rebuilding is rebuilt by obtaining other encoded dataslices of the set of encoded data slices from other online storage unitsof the set of storage units. Note the rebuilding may be done by thenewly online storage unit or another computing device (e.g., otherstorage unit, DS processing unit, managing unit, etc.) of the DSN.

At time T2, a computing device of the DSN determines the selectivelybringing online and taking offline storage units (e.g., according to aDSN protocol) indicates that storage units 1, 3, 4, 5, 6 and 8 are to beonline and storage units 2 and 7 are to be offline. The computing devicebrings the first and sixth storage units online (e.g., by sending anactivate message, a command, etc.) and determines a rebuilding approachfor the first and sixth storage units. The rebuilding approach includesan expedited rebuilding procedure, a normal rebuild procedure, a fullrebuilding technique (e.g., a rebuilding agent reconstructs a datasegment and re-encodes it to produce a rebuilt slice), and/or a partialrebuilding. The partial rebuilding approach includes each storage unitof a decode threshold number of storage units performing a two-stepprocess to generate partial slice rebuilding data. In the first step, astorage unit performs a partial decoding of an encoded data slice of aset of encoded data slices using selected rows of the decoding matrix.This produces a partial decode matrix. In the second step, the storageunit matrix multiplies the partial decode matrix with a reduced encodematrix to produce the partial slice rebuilding data. A function (e.g.,an exclusive OR function) is performed on the partial slice rebuildingdata to generate a rebuilt encoded data slice.

When the rebuilding approach is the expedited rebuilding procedure thecomputing devices sends a command to the first storage unit to rebuildencoded data slices at an accelerated rate in comparison to the normalrate. For example, the normal rate of rebuilding consumes 5-10% ofprocessing resource of a device (e.g., storage unit, computing device,etc.) and the accelerated rate consumes greater than 10% of theprocessing resources.

In addition to determining a rebuilding process, the computing devicedetermines a transition approach for taking storage units offline; inthis example, taking storage units 2 and 7 off line. To render thisdecision, the computing device gathers data regarding the encodingparameters (e.g., decode threshold, write threshold, read threshold, andpillar width), amount of data written into the DSN since the lasttransition, an estimated time to rebuild encoded data slices, systemreliability, and/or system use levels. For example, the computing devicedetermines to take both storage units 2 and 7 offline as soon as storageunits 1 and 6 are back on line when the system use level is relativelylow, system reliability is high, the amount of time to rebuild encodeddata slices is low, and there will be a write threshold number ofstorage units still online. As another example, the computing devicedetermines to leave one or both of storage units 2 and 7 online untilone or both of storage units 1 and 6 have had their respective encodeddata slices rebuilt when the conditions are different than in thepreceding example.

At time T3, a computing device of the DSN determines the selectivelybringing online and taking offline storage units indicates that storageunits 1, 3, 6 and 7 are to be online and storage units 2, 4, 5 and 8 areto be offline. Thus, the computing device brings online storage unit 7and determines a rebuilding approach for encoded data slices that arestored or to be stored in the storage unit 7. For example, the computingdevice determines that once storage units 4, 5 and 8 are taken offline,four storage units (e.g., SU #1, 3, 6 and 7) will be online, which isless than the write threshold and at the read threshold. Thus, thecomputing device may keep one or more of storage units 4, 5 and 8 onlinewhile encoded data slices stored or to be stored in SU #7 are rebuilt.Note the computing device may also restrict one or more of storage units4, 5 and 8 from going offline while storage units 4, 5 and 8 are storingdata that is needed for a rebuilding process in other storage units ofthe set of storage units.

Note that during time T3, a write threshold number of storage units arenot online. Thus, the set of storage unit may perform reads but may notperform a write operation during this time, and the computing device maydetermine to perform expedited rebuilding upon bringing online storageunits 2 and 4 for time t4. Alternatively, the computing device maydetermine to adjust the write threshold (e.g., lowering the writethreshold to 4 for time period t3). Further alternatively, a DSprocessing unit may determine to cache encoded data slices to be storedin storage unit 4 for time t3 to continue writing processes. The DSprocessing unit may then, at time t4, send an activation message tostorage unit 4 with encoded data slices to be stored in storage unit 4.

At time T4, a computing device of the DSN determines the selectivelybringing online and taking offline storage units indicates that storageunits 1, 2, 4, 6 and 7 are to be online and storage units 3, 5 and 8 areto be offline. At time T5, a computing device of the DSN determines theselectively bringing online and taking offline storage units indicatesthat storage units 1, 2, 4, 5, 7 and 8 are to be online and storageunits 3 and 6 are to be offline.

FIG. 13 is a flowchart of a method of an example of rotating offlinestorage units of a dispersed storage network (DSN). The method beginswith step 160, where a computing device of the DSN selectively bringsonline and takes offline storage units of a set of storage units of theDSN. When bringing a first storage unit of the set of storage unitsonline and taking a second storage unit of the set of storage unitsoffline in accordance with the selectively bringing online and takingoffline storage units, the method continues with step 162 where thecomputing device determines a rebuilding approach of the first storageunit and a first to second storage unit transition.

The method continues with step 164, where the computing device bringsthe first storage unit online in accordance with the rebuilding approachand the first to second storage unit transition. As an example of thedetermining the rebuilding approach and the first to second storage unittransition, when the number of online storage units is at or below aread threshold once the second storage unit is offline, the computingdevice may determine to rebuild an encoded data slice of the firststorage unit before the second storage unit goes offline. As anotherexample of the determining the rebuilding approach and the first tosecond storage unit transition, when the number of online storage unitsis at or above a write threshold once the second storage unit isoffline, the computing device may determine to rebuild an encoded dataslice of the first storage unit after the second storage unit goesoffline.

The method continues with step 166, where the computing device takes thesecond storage unit offline in accordance with the first to secondstorage unit transition. As an example, the computing device keeps thesecond storage unit online (e.g., according to a rotating prioritylevel, a DSN protocol, a change to the selectively taking offline andbringing online storage units, etc.). As another example, the computingdevice may take the second storage unit offline after data of the firststorage unit is rebuilt. As yet another example, the computing devicemay take the second storage offline once the first storage unit isonline.

As another example, when bringing the first storage unit and a thirdstorage unit of the set of storage units online and taking the secondstorage unit and a fourth storage unit of the set of storage unitsoffline, in accordance with the selectively bringing online and takingoffline storage units, the computing device determines a secondrebuilding approach of the first and third storage units and a first andthird to second and fourth storage unit transition.

Next, the computing device brings the first and third storage unitsonline in accordance with the second rebuilding approach and the firstand third to second and fourth storage unit transition and takes thesecond and fourth storage units offline in accordance with the first andthird to second and fourth storage unit transition. In this example, thecomputing device concurrently rebuilds according to the secondrebuilding approach and the third to second and fourth storage unittransition, one or more sets of encoded data slices of the first andthird storage units that need rebuilding.

It is noted that terminologies as may be used herein such as bit stream,stream, signal sequence, etc. (or their equivalents) have been usedinterchangeably to describe digital information whose contentcorresponds to any of a number of desired types (e.g., data, video,speech, audio, etc. any of which may generally be referred to as‘data’).

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “configured to”, “operably coupled to”, “coupled to”, and/or“coupling” includes direct coupling between items and/or indirectcoupling between items via an intervening item (e.g., an item includes,but is not limited to, a component, an element, a circuit, and/or amodule) where, for an example of indirect coupling, the intervening itemdoes not modify the information of a signal but may adjust its currentlevel, voltage level, and/or power level. As may further be used herein,inferred coupling (i.e., where one element is coupled to another elementby inference) includes direct and indirect coupling between two items inthe same manner as “coupled to”. As may even further be used herein, theterm “configured to”, “operable to”, “coupled to”, or “operably coupledto” indicates that an item includes one or more of power connections,input(s), output(s), etc., to perform, when activated, one or more itscorresponding functions and may further include inferred coupling to oneor more other items. As may still further be used herein, the term“associated with”, includes direct and/or indirect coupling of separateitems and/or one item being embedded within another item.

As may be used herein, the term “compares favorably”, indicates that acomparison between two or more items, signals, etc., provides a desiredrelationship. For example, when the desired relationship is that signal1 has a greater magnitude than signal 2, a favorable comparison may beachieved when the magnitude of signal 1 is greater than that of signal 2or when the magnitude of signal 2 is less than that of signal 1. As maybe used herein, the term “compares unfavorably”, indicates that acomparison between two or more items, signals, etc., fails to providethe desired relationship.

As may also be used herein, the terms “processing module”, “processingcircuit”, “processor”, and/or “processing unit” may be a singleprocessing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may be, or furtherinclude, memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of another processing module, module, processing circuit,and/or processing unit. Such a memory device may be a read-only memory,random access memory, volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

One or more embodiments have been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claims. Further, the boundariesof these functional building blocks have been arbitrarily defined forconvenience of description. Alternate boundaries could be defined aslong as the certain significant functions are appropriately performed.Similarly, flow diagram blocks may also have been arbitrarily definedherein to illustrate certain significant functionality.

To the extent used, the flow diagram block boundaries and sequence couldhave been defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claims. One of average skill in the art will alsorecognize that the functional building blocks, and other illustrativeblocks, modules and components herein, can be implemented as illustratedor by discrete components, application specific integrated circuits,processors executing appropriate software and the like or anycombination thereof.

In addition, a flow diagram may include a “start” and/or “continue”indication. The “start” and “continue” indications reflect that thesteps presented can optionally be incorporated in or otherwise used inconjunction with other routines. In this context, “start” indicates thebeginning of the first step presented and may be preceded by otheractivities not specifically shown. Further, the “continue” indicationreflects that the steps presented may be performed multiple times and/ormay be succeeded by other activities not specifically shown. Further,while a flow diagram indicates a particular ordering of steps, otherorderings are likewise possible provided that the principles ofcausality are maintained.

The one or more embodiments are used herein to illustrate one or moreaspects, one or more features, one or more concepts, and/or one or moreexamples. A physical embodiment of an apparatus, an article ofmanufacture, a machine, and/or of a process may include one or more ofthe aspects, features, concepts, examples, etc. described with referenceto one or more of the embodiments discussed herein. Further, from figureto figure, the embodiments may incorporate the same or similarly namedfunctions, steps, modules, etc. that may use the same or differentreference numbers and, as such, the functions, steps, modules, etc. maybe the same or similar functions, steps, modules, etc. or differentones.

Unless specifically stated to the contra, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, and single-endedor differential. For instance, if a signal path is shown as asingle-ended path, it also represents a differential signal path.Similarly, if a signal path is shown as a differential path, it alsorepresents a single-ended signal path. While one or more particulararchitectures are described herein, other architectures can likewise beimplemented that use one or more data buses not expressly shown, directconnectivity between elements, and/or indirect coupling between otherelements as recognized by one of average skill in the art.

The term “module” is used in the description of one or more of theembodiments. A module implements one or more functions via a device suchas a processor or other processing device or other hardware that mayinclude or operate in association with a memory that stores operationalinstructions. A module may operate independently and/or in conjunctionwith software and/or firmware. As also used herein, a module may containone or more sub-modules, each of which may be one or more modules.

As may further be used herein, a computer readable memory includes oneor more memory elements. A memory element may be a separate memorydevice, multiple memory devices, or a set of memory locations within amemory device. Such a memory device may be a read-only memory, randomaccess memory, volatile memory, non-volatile memory, static memory,dynamic memory, flash memory, cache memory, and/or any device thatstores digital information. The memory device may be in a form a solidstate memory, a hard drive memory, cloud memory, thumb drive, servermemory, computing device memory, and/or other physical medium forstoring digital information.

While particular combinations of various functions and features of theone or more embodiments have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent disclosure is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. A method comprises: selectively, by a computingdevice of a dispersed storage network (DSN), bringing online and takingoffline storage units of a set of storage units of the DSN; whenbringing a first storage unit of the set of storage units online andtaking a second storage unit of the set of storage units offline inaccordance with the selectively bringing online and taking offlinestorage units, determining, by the computing device, a rebuildingapproach of the first storage unit and a first to second storage unittransition; bringing, by the computing device, the first storage unitonline in accordance with the rebuilding approach and the first tosecond storage unit transition; and taking, by the computing device, thesecond storage unit offline in accordance with the first to secondstorage unit transition.
 2. The method of claim 1, wherein theselectively bringing online and taking offline storage units comprisesone or more of: a scheduled timeframe; an amount of power consumed by astorage unit of the set of storage units; an amount of data written to astorage unit of the set of storage units; restricting taking offline astorage unit that includes an encoded data slice that needs rebuilding;restricting taking offline a storage unit that includes an encoded dataslice that is critical to a rebuilding of another encoded data slice;and determining a storage unit of the set of storage units will not beavailable during a scheduled online timeframe.
 3. The method of claim 1,wherein the rebuilding approach comprises one or more of: an expeditedrebuilding procedure; a normal rebuild procedure; a full rebuildingtechnique; and a partial rebuilding technique.
 4. The method of claim 1,wherein the first to second storage unit transition comprises one of:keeping the second storage unit online; taking the second storage unitoffline after data of the first storage unit is rebuilt; and taking thesecond storage offline once the first storage unit is online.
 5. Themethod of claim 1, wherein the determining the rebuilding approach andthe first to second storage unit transition comprises one of:determining one or more encoded data slices of the first storage unitneeds to be rebuilt before the second storage unit goes offline when anumber of online storage units is at or below a read threshold once thesecond storage unit is offline; and determining one or more encoded dataslices of the first storage unit does not need to be rebuilt before thesecond storage unit goes offline when the number of online storage unitsis at or above a write threshold once the second storage unit isoffline.
 6. The method of claim 1 further comprises: when bringing thefirst storage unit and a third storage unit of the set of storage unitsonline and taking the second storage unit and a fourth storage unit ofthe set of storage units offline, in accordance with the selectivelybringing online and taking offline storage units, determining, by thecomputing device, a second rebuilding approach of the first and thirdstorage units and a first and third to second and fourth storage unittransition; bringing, by the computing device, the first and thirdstorage units online in accordance with the second rebuilding approachand the first and third to second and fourth storage unit transition;and taking, by the computing device, the second and fourth storage unitsoffline in accordance with the first and third to second and fourthstorage unit transition.
 7. The method of claim 6 further comprises:concurrently rebuilding, according to the second rebuilding approach andthe third to second and fourth storage unit transition, one or more setsof encoded data slices of the first and third storage units that needrebuilding.
 8. A computing device of a dispersed storage network (DSN)comprises: memory; an interface; and a processing module operablycoupled to the interface and memory, wherein the processing module isoperable to: selectively bring online and take offline storage units ofa set of storage units of the DSN; when bringing a first storage unit ofthe set of storage units online and taking a second storage unit of theset of storage units offline in accordance with the selectively bringingonline and taking offline storage units, determine a rebuilding approachof the first storage unit and a first to second storage unit transition;bring the first storage unit online in accordance with the rebuildingapproach and the first to second storage unit transition; and take thesecond storage unit offline in accordance with the first to secondstorage unit transition.
 9. The computing device of claim 8, wherein theprocessing module is operable to selectively bring online and takeoffline storage units according to one or more of: a scheduledtimeframe; an amount of power consumed by a storage unit of the set ofstorage units; an amount of data written to a storage unit of the set ofstorage units; restricting taking offline a storage unit that includesan encoded data slice that needs rebuilding; restricting taking offlinea storage unit that includes an encoded data slice that is critical to arebuilding of another encoded data slice; and determining a storage unitof the set of storage units will not be available during a scheduledonline timeframe.
 10. The computing device of claim 8, wherein theprocessing module is operable to perform the rebuilding approach by oneor more of: an expedited rebuilding procedure; a normal rebuildprocedure; a full rebuilding technique; and a partial rebuildingtechnique.
 11. The computing device of claim 8, wherein the processingmodule is operable to perform the first to second storage unittransition by one of: keeping the second storage unit online; taking thesecond storage unit offline after data of the first storage unit isrebuilt; and taking the second storage offline once the first storageunit is online.
 12. The computing device of claim 8, wherein theprocessing module is operable to determine the rebuilding approach andthe first to second storage unit transition by one of: determining datawithin the first storage unit needs to be rebuilt before the secondstorage unit goes offline when a number of online storage units is at orbelow a read threshold once the second storage unit is offline; anddetermining data within the first storage unit does not need to berebuilt before the second storage unit goes offline when the number ofonline storage units is at or above a write threshold once the secondstorage unit is offline.
 13. The computing device of claim 8, whereinthe processing module is further operable to: when bringing the firststorage unit and a third storage unit of the set of storage units onlineand taking the second storage unit and a fourth storage unit of the setof storage units offline, in accordance with the selectively bringingonline and taking offline storage units, determine, a second rebuildingapproach of the first and third storage units and a first and third tosecond and fourth storage unit transition; bring the first and thirdstorage units online in accordance with the second rebuilding approachand the first and third to second and fourth storage unit transition;and take the second and fourth storage units offline in accordance withthe first and third to second and fourth storage unit transition. 14.The computing device of claim 13, wherein the processing module isfurther operable to: concurrently rebuild, according to the secondrebuilding approach and the third to second and fourth storage unittransition, one or more sets of encoded data slices of the first andthird storage units that need rebuilding.